The use of devices to sift siftable or particulate material to remove relatively larger items found in the material is well known. Sifting devices enjoy a wide range of uses, from separating aggregates and other granular materials in quarry or concrete mixing operations, to sifting ingredients for baked foods, to use with pet litter boxes.
With pet litter boxes, screens of various sorts have been employed for removing solid excrement deposited in pet litter and sand in place of the traditional method of using a hand-held scoop or strainer. Sifting devices not only reduce the unpleasantness of the operation, but they reduce waste by minimizing the amount of unused litter being thrown out, and so more litter is reused. Examples of such devices are shown in U.S. Pat. Nos. 3,796,188, 4,217,857, 4,505,226, 4,602,593, 4,615,300 and 4,771,731. However, these prior art litter box devices are impractical and cumbersome to use and are unduly complex to make because of the various movable flaps, plates and false bottoms. They also waste time. In many cases, the screens are used in combination with imperforate pans to trap the litter.
It is therefore desired to provide a sifting device having a series of stacked trays adapted to hold a quantity of siftable material. Each of these trays being bereft of movable parts, yet being capable of sifting the material when lifted off of the stack.